The macrolactone archazolid is a novel, highly specific V-ATPase inhibitor with an IC 50 Vacuolar ATPases (V-ATPases)3 are heteromultimeric proteins that use the energy of ATP hydrolysis to translocate protons from the cytoplasm into intracellular compartments or across the plasma membrane of eukaryotic cells. This transport of protons is mediated by the membrane-integral V O complex, whereas the cleavage of ATP occurs at the cytoplasmatic V 1 complex (1). The V O complex is composed of single copies of subunits a, d, and e, and the ring-forming proteolipid subunits c, cЉ, and in fungi subunit cЈ also (2). Based on the crystal structure from the V O ring of K subunits, a homologue of the H ϩ -translocating subunit c in the V-type Na ϩ -ATPase from Enterococcus hirae, and a cryoelectron microscopy structure from the V-ATPase of Manduca sexta, an arrangement of 10 subunits is proposed for the V O ring (3, 4). The subunits c and cЈ are predicted to have four transmembrane helices (TM 1 to 4), whereas subunit cЉ contains an additional fifth transmembrane helix. All proteolipid subunits contain a conserved glutamate residue, subunits c and cЈ in TM4 and subunit cЉ in TM3, which are essential for proton transport across the membrane (2). This glutamate is a target for the covalent binding inhibitor N,NЈ-dicyclohexylcarbodiimide (DCCD) and its derivatives (5-8).By regulating the pH homeostasis and membrane energization of cells, V-ATPases are involved in a variety of fundamental processes like vesicular trafficking or secondary transport. In addition, plasma membrane V-ATPases are responsible for extracellular acidification, e.g. in osteoclasts or metastasing tumor cells, and therefore play an important role in severe diseases such as osteoporosis or cancer (7). For these reasons the V-ATPase is a promising therapeutic target, and inhibitors of this enzyme are the focus of biomedical research. A variety of such compounds has been discovered of which the plecomacrolide inhibitors bafilomycin and concanamycin are the best studied examples (9). With IC 50 values at low nanomolar concentrations these compounds are highly specific inhibitors of the V-ATPase (10). Throughout the past years the binding site and inhibition mechanism of the plecomacrolides has been studied in more detail. In 2002 Bowman et al. (11) identified via mutagenesis studies in Neurospora crassa amino acids in V O subunit c that contribute to the binding of bafilomycin. In the same year photoaffinity labeling studies with the radioactive concanamycin derivative 125 I-concanolid A also resulted in the *

The archazolids are complex polyketides isolated from the myxobacterium Archangium gephyra and are potent inhibitors of vacuolar type ATPases. Herein, we report the first total synthesis of archazolid A, which establishes unequivocally the relative and absolute configuration of this macrolide antibiotic. Key features of our synthesis include an aldol condensation for construction of the delicate (Z,Z,E)-triene-system, an E-selective Heck reaction on a highly elaborate substrate, and a HWE macrocyclization to close the 24-membered macrolactone.

A modular total synthesis of the potent V-ATPase inhibitors archazolid A and B is reported. The convergent preparation was accomplished by late-stage diversification of joint intermediates. Key synthetic steps involve asymmetric boron-mediated aldol reactions, two consecutive Still-Gennari olefinations to set the characteristic (Z,Z)-diene system, a Brown crotyboration, and a diastereoselective aldol condensation of highly elaborate intermediates. For macrocyclization, both an HWE reaction and a Heck coupling were successfully employed to close the 24-membered macrolactone. During the synthetic campaign, a generally useful protocol for an E-selective Heck reaction of nonactivated alkenes and a method for the direct nucleophilic displacement of the Abiko-Masamune auxiliary with sterically hindered nucleophiles were developed. The expedient and flexible strategy will enable further SAR studies of the archazolids and more detailed evaluations of target-inhibitor interactions.

[reaction: see text] A novel, biomimetic concept for the direct reductive amination of ketones is described that relies on selective imine activation by hydrogen bond formation. The mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor and utilizes the Hantzsch ester for transfer hydrogenation. The method allows the efficient synthesis of structurally diverse amines.

Scheme 4. Assembly of the C23-C29 subunit 4. Bn= benzyl, Mes = 2,4,6-trimethylphenyl, PDC = pyridinium dichromate.Scheme 5. Completion of the total synthesis. dppf = diphenylphosphinoferrocene, TCBC = 2,4,6-trichlorobenzoyl chloride, TBAF = tetra-nbutyl ammonium fluoride. AngewandteChemie 5669

An efficient procedure for the directed reductive amination of beta-hydroxy-ketones (3) for the stereoselective preparation of 1,3-syn-amino alcohols (6) is reported. The operationally simple protocol uses Ti(iOPr)4 for coordination of the intermediate imino alcohol (5) and PMHS as the reducing agent. The method was expanded to an asymmetric aldol reductive amination sequence to allow a highly convergent synthesis of the hydroxy-amine core of the HIV-protease inhibitors ritonavir and lopinavir. [reaction: see text].

A highly convergent synthesis of the central dimeric core of the potent antibiotic macrolide rhizopodin is reported. Notable features of the highly concise route include an effective preparation of the key C8-C22 building block based on an iridium-catalyzed Krische allylation and a chemoselective cross-coupling approach toward the macrocycle involving a highly advantageous Heck reaction for macrocyclization.

No abstract